There is more than one, typically called Rayon I, Rayon II, Rayon III per inscriptions. "Rayon" was the category based on weight and distance sent. 2 genuine are shown here:
https://goscf.com/t/65080History and pics:
https://en.wikipedia.org/wiki/Local..._SwitzerlandThese are among the earliest stamps. Like other classics, expensive used is based on being sound, 4 large margins, reasonable cancel. Mint ones are much rarer and have to have full OG to merit a big price. Pen cancels on used drop the price greatly, as does any stamp with less than 4 margins. Faults reduce the price tremendously.
The issues are forged but there are references to detect them. Forgeries are found frequently enough; they are often hard to tell unless you have an original or references. Even then, forgeries can be very convincing. The basic detection method is to compare against the known plate positions (photos exist) and if they match, it's genuine. The exception would be the Sperati forgeries of these which I believe were photographically reproduced from original stamps. Still, there are characteristics there than can separate the Sperati forgeries.